Anti-arcing safety switch



Jan. 19, 1960 B. v. CARLSON ETAL 2,921,995

ANTI-ARCING SAFETY SWITCH 2 Sheets-Sheen 1 Filed Jan. 8, 1958 Y N M K E OSL N TLOA R RP O AE T CD T N A E l6 TR R L EE BGW Jan. 19, 1960 B. v. CARLSON ETAL 2,921,995

ANTI-ARCING SAFETY SWITCH 2 Sheets-Sheet 2 Filed Jan. 8, 1958 ATTORNEY United States Patent 2,921,995 ANTI-ARCING SAFETY swrrcrr Bertil V. Carlson, George J. Depold, and Willmer N.

Stark, Livermore, Califi, assignors, by mesne assignments, to Librascope, Incorporated, a corporation of California Application January 8, 1958, Serial No. 707,811

4 Claims. (Cl. 200-) objections.

Another object of this invention is to provide a novel safety switch which is reliable, capable of being compressed into an extremely small and compact package, and which can be varied in design for various loads and conditions and can still be completely arc-less.

Briefly described, our invention comprises a rotary switch, that is entirely self-contained. It can be manually or motor operated. A pair of spaced apart low resistance bus bar contacts are each integrally and electrically connected to a separate shaped resistance element and a slidingcontact arm which rotates from one bus bar contact to the other, and at the same time slidably contacts the shaped resistance elements.

As the switch contact moves from one bus contact to the other, it is substantially simultaneously in contact with both the shaped resistances, thereby instantaneously providing a short across the switch contact points immediately upon the break, and thus preventing arcing. As the switch contact continues to rotate away from one bus contact and toward the other, it picks up contact with the shaped resistance of the opposite bus bar and continues until it gradually breaks contact with the first shaped resistance just prior to making positive contact with the opposite bus bar contact, thus eliminating abrupt power drop between the contact points.

Other objects and advantages of this invention will become apparent as the discussion proceeds and are taken in connection with the accompanying claims and drawings in which:

Figure 1 is a diagrammatic view explaining the basic principle embodying our invention;

Figure 2 shows a top plan view partially broken away and in section of one form of switch embodying our invention;

Figure 3 shows a side plan view partially in section embodying our invention, and;

Figure 4 shows an exploded view of a complete motor actuated switch embodying our invention with'certain parts cut away to clearly illustrate the operation and manner of assembly of the switch embodying our invention.

Turning now to a detailed description of our invention in-Figure 1, showing in principle the operation of our invention, the numerals 10 and 11 refer generally to bus bar contacts. These contacts 10 and 111 are more or less of conventional material, such as copper, bronze, silver, or the like. Attached to the bus bar contact 10 is a shaped resistance 12 and to the bus bar 11 is a second similarly shaped resistance 13. The general overall shape of the resistances 12 and 13, as shown in Figure 1, is that of a wedge, with the base or heavy portion of'the resistance being electrically and directly connected to the bus bar. The resistance material of the shaped resistances 12 and 13 is not of particular importance in practicing our invention, however carbon blocks of relatively low resistance, or the like, are preferable.

A sliding contact 14 is connected to a load 15 by means of a bar 16. The load 15, by way of illustration for the purpose of explaining the operation of this switch, is connected to one side of a power source 17, which power source in turn is connected to bus bar contact 10. In parallel with power source 17 is a second power source 18 which is connected at one side of the load 15 and the opposite side to bus bar contact 11. The common contacts of the load 15, power source '17 and power source 18, as desired, may be grounded, as shown.

In operation, the sliding contact 14 is closed against bus bar contact 10. As will be seen in Figure 1, this makes a complete circuit through load 15 from power source 17. As it is desired to switch from power source 17 to power source 18, the sliding contact 14 is moved toward bus bar contact 11.

Sliding contact 14 is in sliding contact with both shaped resistances 12 and 13 at the same time, except for the short distance at the extreme ends of each resistance, and is in contact with shaped resistance 12, at the same time it is in contact with the bus bar 10. As it breaks the circuit from bus bar 10, current flows through contact 14 into shaped resistance 12, thence through bus 10 and back to the power source 17. At this point in the eX-' planation of the operation of our invention, it is pointed out that the particular substance used in the shaped resistances 12 and 13 must be of a substantially low resistance, such as a carbon pile, or the like, so that When the mass and cross section thereof is electrically comparable to that of the contacting bus 11 or 12, the voltage drop across the contact points between 10 and id, or 11 and 14, will at the moment of break be at a minimum.

As is illustrated in Figure l, the shaped resistances 12 and 13 are'illustrated as being wedge shaped. However, it is to be understood that specific geometric configuration of these resistances can be varied for specific designs, without departing from the spirit of our invention. These resistances must be so shaped as to increase in resistance as the end opposite its connected bus bar is approached and, of course, conversely as the bus is approached the resistances 12 and 13 must decrease in resistance.

Continuing now with the explanation of the operation of the principle embodying our invention, as the sliding contact 14 continues to move, toward the right in Figure 1, or toward the opposite bus bar contact 11, the amount of current conducted through the switch from the power supply 17 to the load 15 decreases.

After sliding contact 14 continues to move along the shaped resistance 12, contact is picked up and made with the end of shaped resistance 13 lying opposite bus bar contact 11. At this point of contact with shapedresistance 13, current begins to flow from the second power source 18 into load 15, and after contact 14 continues to move along the shaped resistance 12 and the shaped resistance 13 toward the bus bar contact 11, less current flows from power source 17 to load 15, and more current from power source 18 flows to load 15, until the end of shaped resistance '12 isreached. This occurs 'just before contact is made with bus bar 11, at which time power from source 17 is completely cut off and momentarily before contact between bus bar 11 and sliding contact 14,,-and provides avery low, resistance shuntingacross these contact points through the shaped resistance 13. Fromitheforegoing, it will be seen that we have provided a fswitchwhich prevents arcing across the contacts, and at the same time permits a gradual changing of power supply on a load fromone source to another without abruptly closing the circuit on one source and opening the circuit from the other source, and, at the same time also provides a switch which makes it impossible tooverload the circuit by throwing in'the full loadof both power sources at the same time.

Turning now to a detailed description switch embodying our invention in Figures 2 and 3, the numeral 20 designates generally a casing or housing made of suitable insulating'material, and which preferably is icapable of being sealed air tight. A first bus bar contact 21 is attached in any suitable manner to the wall of the cylindrical casing 20, and a second bus bar contact 22 is mounted on the wall of the cylindrical casing 20, as best shown in Figure 2. If desired, a suitable insulation 23 Separating the bus bar contacts 21 and 22 can be provided. Securely mounted upon and electrically connected to bus bar 21 is a shaped resistance '24. A similarly shaped resistance is'mounted upon and electrically connected 'to bus bar 22. Each of the shaped resistances 24 and 25 are securely attached to their respective bus bars 21 and 22 by means of suitable bolts 26. Rotatably mounted within the casing 20 is a sliding contact, or rotatable switch arm, designated generally by the numeral 27. As better shown in the exploded view of Figure 4, the contact 27 consists of an insulation member 28 provided with a recess, or cavity, 29, therein into which contact brushes 30 are slidably inserted. Contact brushes 30 preferably are made of sintered bronze or copper, or other desirable maof one form of terial satisfactory for slidable contact with a resistance A material. On one end of each of the contact brushes 30 a is a sheath 31 of material suitable for sliding contact with a bronze or brass collector ring 32. I

Springs 33 of a conventional nature and design urge the contact brushes 30 outward against the shaped resistances 24 and 25. As shown in both Figure 2 and Figure 4, sliding contact 27 is provided with a pair of switch contacts 34, preferably made of copper, silver,

mounted for support in end plate 38, and the bottom of the two bearings 37 is mounted in an intermediately lo cated plate 39, as best shown in Figure 3. The lower end of shaft 36 is provided with a square shoulder coupling 40, which in turn fits into a female coupling 41 of shaft 42. Shaft 42 is connected to a high torque motor 43,

which may be of conventional design and the details I of which are unnecessary to explain for. the purpose of a clear understanding of this invention. Suffice it to say that the high torque motor 43 is reversible and has a drive through an arc of at least forty-five degrees. A semicylindrical insulation 44, as best shown in Figures 2 and 4, is provided to give support to the shaped'resistance element 24, and at the same time permit the contact brushes 30 to be held in place when they are not hearing against the shaped resistance elements 24 or 25.

- An insulating spacing ring 45 is provided between the end plate 38 and the top side of the bus bars 21 and 22, the shaped resistance elements 24 and 25, and the semicylindrical insulating material 44. An insulating ring 46 is provided between the bus bars 21 and 22, the, shaped resistanceelements 24 and 25 and the semi-cylindrical insulation 44., As desired a shoulder 47 can be provided on the insulating ring 46. The collector ring 32 preferably is se mi-circular in shape, as shown in Figure 4, and is contoured as at 48 on the inner periphery thereof to have the same configuration as the inner periphery of bus bars 21 and 22, and shaped resistance elements 24 and 25.

A second insulating ring 49 is provided, as shown, to space collector ring 32 from the intermediate plate 39. A motor bearing 50 supports the shaft 42; An electrical connecting plug 51 extends through the wall of the eyliri- (irical casing 251 andprovides' external power; Contact for bus bar 21, while plug 52 extends through the wall of the cylindrical housing 20 and, provides electrical contact to the second power supply. Plug 53 passes through the wall of cylindrical housing 20 and engages the collector ring 32 for electrical contact with the load. I

Referring back to the schematic diagram in Figure 1, bus bar contact 21 is comparable to bus bar contact 11, bus bar contact 22 is comparable to bus bar'contact 10, shaped resistance element 24 is comparable to shaped re sistance 13 and shaped" resistance element'25 is comparable to shaped resistance 12. The rotatableswitch arm '27. is comparable to the sliding contact l4 and the electrical connecting plug 51 is preferably connected to the power source comparable to source 18, plug 52 to power source 17 and'plug 53 to load 15. a K a I g The operation of the preferredembodimentofour invention, shown in Figures 2, '3 and '4, is identical to the operation explained'inFigure 1. When the switch is in the position shown in Figure 2, the contact 34 is closed against a bus .bar 22', and current passes from contact 34 through the bus 22, the connector'plugf52 into the power supply, back through the load and into the collector ring 32, thence from the sliding contact back to the contact 34. As the rotatable switch arm 27' is rotated in a clockwise direction, the contact brush 30is in contact with the shaped resistance element 25, which, adjacent its connection to bus 22, as can bestbe seen'in Figure 2, is relatively. large'in cross section. The instant the contact 34 is broken from the bus 22, current flows from the bus 22 through shaped resistance element 25 into the contact brush 30 and thence into collector ring 32. With the resistance of the shaped resistance element'25 in this area' being relatively low, a relatively low-potential acrossthe contact points between contact 34 andbus 22 will beheld below the level at'which the brushes will arc. As the rotatable switch arm 27 continues to rotate in a clockwise direction, the contact br ush 30 makes contact with the shapedresistance element'24, and because of the small cross sectional area 'of the shaped resistance element '24 at this point, the'resistance to electrical current will behigh, but as the rotatable switchfarm 27 continues to rotate, the resistance in shaped resistance element 25 increases and the resistance in shaped resistance element 24 decreases, until the contact brush 30 making contact with the shaped resistance element 24 :begins to approach, and just before the contact 34 makes contact 7 with bus 21, the resistance of the cross sectional area of the shaped resistance element 24 is suflicientlylarge so that the resistance across the pointsjof contact 34 and bus 21 is relatively very'low, which in turn would eliminate any possibility of sparking between the contact points prior to the closingof-the contacts. 7 "i It will be appreciated from the foregoing that'the par ticular cross sectional area at any one;pla ce'-infthe shaped resistance elements 24 and 25 and;the particular resistance material thereof will of necessity vary -as" a design characteristic for varying loads and capacities to Y which each switch is made; Furthermore, the cross'sectional area of the shaped resistance element 24 can be varied by contouring the. rear faces 54 and 55 of each shaped resistance, as also shown in Figure-3. The specific size of the bus bar contacts 21 and 22 also will vary according to the design for the specific load forwhich the switch is'being "made, but it is; pointed out-that it is deemed preferable to in all instances make the busses 21 and 22 of relatively heavy duty. Furthermore, as desired, the cylindrical casing 20 can be terminated at the intermediate plate 39 and the switch can be manually operated by putting a suitable hand knob on the square shoulder 41 and the high torque motor 43 eliminated. On the other hand, it is to be understood that if it is desired to have the high torque motor 43 drive other equipment, the shaft 36 could be extended through the bearing 37 and the end plate 38, with the housing 20 suitably extended. It is also to be understood that other changes in material and size can be resorted to without departing from the spirit of our invention, which is set forth in the appended claims.

We claim:

1. An anti-arcing rotary safety switch comprising a pair of bus bar contacts, an arcuate shaped resistance element connected to each of said bus bar contacts, each of said shaped resistance elements being of such a shape that the mass per unit length, the cross sectional area of said resistance element, and the efiective contact area of each vary with the distance from each of said bus bars and a rotary switch arm alternately engaging said bus bar contacts and slidably engaging each of said shaped resistance elements intermediate its movement from one bus bar contact to the other.

2. An anti-arcing rotary safety switch comprising a pair of bus bar contacts, an arcuate shaped resistance element connected to each of said bus bar contacts, each of said shaped resistance elements being of such a shape that the mass per unit length, the cross sectional area of said resistance element, and the eifective contact area of each vary with the distance from each of said bus bars, said shaped resistance elements having a large mass and a minimum resistance adjacent its end connected to its bus bar contact and decreasing in mass and increasing in resistance at its end opposite its connected bus bar contact, and a rotary switch arm alternately engaging said bus bar contacts and engaging each of said shaped resistance elements intermediate its movement from one bus bar contact to the other.

3. An anti-arcing rotary safety switch comprising a pair of bus bar contacts, an arcuate shaped resistance element mounted upon and connected to each of said bus bar contacts, each of said shaped resistance elements be ing of such a shape that the mass per unit length, the

cross sectional area of said resistance element, and the effective contact area of each vary with the distance from each of said bus bars, each of said shaped resistance elements being wedge shaped with its base of greater mass 1 and lowest resistance being connected to said bus bar contact and decreasing in mass and increasing in resist ance opposite its base and disposed away from said bus bar contact and a rotary switch arm alternately engaging said bus bar contacts and slidably engaging each of said shaped resistance elements intermediate its movement from one bus bar contact to the other.

4. An anti-arcing rotary safety switch comprising a pair of bus bar contacts, an arcuate shaped resistance element mounted upon and connected to each of said bus bar contacts, each of said shaped resistance elements being of such a shape that the mass per unit length, the cross sectional area of said resistance element, and the eifec tive contact area of each vary with the distance from each of said bus bars, 'each of said shaped resistance elements being curved and wedge shaped with its base of greater mass and lowest resistance being connected to said bus bar contact and decreasing in mass and increasing in resistance opposite its base and disposed away from said bus bar contact and a rotary switch arm alternately engaging said bus bar contacts and simultaneously engaging each of said shaped resistance elements intermediate its movement from one bus bar contact to the other, said rotary switch arm engaging one of said bus bar contacts and the adjacent shaped resistance element at the same instant, whereby current flows through the largest mass of said resistance element across the contact point at the instant the contact between the bus bar and the switch arm is broken and as the flow of current decreases through one resistance element it increases in the other resistance element.

References Cited in the file of this patent UNITED STATES PATENTS 582,772 Zwigbergk May 18, 1897 1,201,418 Achard Oct. 17, 1916 1,558,052 Schurch Oct. 20, 1925 2,755,347 Allison July 17, 1956 2,818,479 Volk Dec. 31, 1957 FOREIGN PATENTS 549,303 France Nov. 15, 1922 

